The present invention relates to hydrocarbon recovery and to the drilling industry and more particularly relates to hydrocarbon-based and ester-based drilling fluids and other fluids used to recover hydrocarbons, which contain cesium phosphate and uses thereof in hydrocarbon recovery operations, such as the drilling and/or completion of a well for the recovery of hydrocarbons or other materials.
In drilling operations, such as the drilling that occurs in oil field operations, such as performed on dry land or offshore using oil platforms, drilling fluids are designed/formulated to serve several functions. These functions include acting as a lubricant to the drill bit to reduce wear and friction during drilling and also to seal the formation surface by forming a filter cake. In the drilling fluid, agents for lubrication typically are present as well as weighting materials in order to achieve a density that typically produces a pressure greater than the surrounding pressure in the well bore. This overpressure is vital for maintaining wellbore stability and well control. The weighting materials can be soluble salts, or finely-ground particles of heavy non-abrasive minerals like barium sulphate (barite). Furthermore, the drilling fluid also typically contains a sealing or fluid loss agent, such as calcium carbonate, polysaccharides, and other polymers, in order to form the filter cake on the formation surface of the well bore. In addition, when the drilling fluids are used during drilling, the drilling fluid will also contain drilling fines, such as shale and sandstone fines.
In the drilling industry, typically water based muds (WBMs), oil-based muds (OBMs), or synthetic-based muds (SBMs) are used in well drilling operations. Water-based muds typically have a continuous water phase into which salts, polymers, and various other chemicals typically are incorporated to create a homogenous blend. With the exception of those based on formate and acetate brines, the water-based drilling fluids may not have operational capabilities suitable for more extreme drilling conditions, such as drilling of deep wells, high pressure/high temperature wells, and the like. Oil-based muds typically include a continuous phase which comprises a hydrocarbon oil (or synthetic oil or ester in the instance of SBMs), a discontinuous phase which typically comprises an aqueous solution, and emulsifiers. Typically, one or more other agents or additives, such as for weight or density, suspension, oil-wetting, lubrication, fluid loss or filtration control, and rheology control, are also included in the oil-based muds.
Once drilling operations have been completed, the well typically is prepared for the completion operations whereby the mud used for drilling is often displaced by a completion fluid. Completion fluids typically are water-based clear fluids and are formulated to the same density as the drilling fluid used to drill the well, in order to retain the hydraulic pressure on the well bore. There are numerous methods of completing a well, amongst which are open hole completions and gravel packed screened systems. The clear fluids are typically halide based brines such as calcium bromide, calcium chloride, and zinc bromide; or organic based brines such as the formate based fluids.
In drilling an oil or gas well, the use of non-aqueous hydrocarbon-based and ester-based drilling fluids should have the inherent advantages of having an external phase fluid in contact with the formation. However, one severe disadvantage to conventional hydrocarbon-based and ester-based drilling fluid is that weighting materials, such as barite, calcium carbonate, or hematite must be added to increase the density of the fluid. These weighting-material solids are capable of inducing formation damage to producing formations. The presence of solids also makes the hydrocarbon-based and ester-based fluids unsuitable for use as completion and workover fluids. The presence of solids in drilling fluids has a negative effect on hydraulics, slowing down drilling rates and creating a risk of fracturing the well bore. Furthermore, high solids levels in drilling fluids can create thick filter cakes and so increase the risk of getting differentially stuck when the drill pipe is stationary for a length of time. The internal aqueous phase of conventional oil-based drilling fluids is typically a concentrated solution of calcium chloride. The presence of high concentrations of chloride salts in oil-based drilling fluids makes then toxic to onshore and inland aquatic environments. The chloride solutions held in invert oil emulsion may also interfere with the nuclear log interpretation during and after drilling.
Thus, the present inventors have determined that there is a need to provide hydrocarbon-based and ester-based drilling and completion/workover fluids that use chloride-free brine and that are preferably solids free or have low solids in the contents in the drilling fluid, in order to avoid the above-mentioned disadvantages.